1. Field of the Invention
Aspects of this invention relate generally to gaskets, and more particularly to a gasket for a molded part and corresponding method for molding and positioning such a gasket within a groove-like undercut on an inner surface of that molded part.
2. Description of Related Art
By way of background, one major concern in the eyewear industry is how to successfully and consistently form a lens retention groove in at least a portion of an inner surface of the rim of an eyewear frame, for subsequently retaining a lens therewithin. Presently, manufacturers typically use a relatively planar “potato chip” insert. With the insert located within an injection mold, the mold is closed about the insert, and the plastic material is injected into the mold. The insert extends into the cavity of the mold to form the lens retention groove. Upon cooling, the insert is pulled or pushed out. Because the insert tends to be relatively rigid compared to the frame material, and because the frame material tends to be at its most fragile state right after cooling, the lip of the retention groove, along with the rest of the frame, has a tendency to become deformed while being pulled or to snap back and create surface marring and stress fractures that are unacceptable under industry standards. This not only produces a high “scrap rate” (often up to twenty-five percent or more due to unacceptable permanent deformation of the frame), but it also limits frame design options to essentially only those that can accommodate the removal of such a relatively rigid insert during the molding process. Furthermore, manufacturers using such inserts tend to be limited to relatively shallow retention grooves, because deeper grooves would not permit withdrawal of rigid inserts without damage and, thus, even higher scrap rates. This challenge has typically been addressed through the use of improved or alternative inserts that are capable of substantially flexing as they are removed from the molded groove, so as to reduce the likelihood of the groove being deformed or the frame damaged. However, such a solution requires the implementation of an entirely new insert, the cost of which some manufacturers simply cannot afford, and still may not eliminate or sufficiently reduce the potential for damage.
Yet another major concern in the eyewear industry, specifically in designing and molding frames, is ensuring that a uniform pressure or force will be applied about the perimeter of each lens, once it is inserted into the frame, so as not to improperly flex the lens and thereby distort its optics or, worse, fracture the lens. This challenge has typically been addressed through the complexity and expense of precision machining and molding, which can still result in unacceptably high scrap rates and/or limit the possible frame and lens designs. More recently, gaskets made of relatively soft material, such as rubber, and positioned within the lens retention grooves of the frame have been proposed; but the challenge and inconvenience there has been positioning such a gasket within the retention groove and retaining it in place while the lens is being positioned therewithin.
In an attempt to solve this particular problem, U.S. Pat. No. 4,921,341 to Ace discloses a safety lens liner adapted to be mounted on the peripheral edge of an eyeglass lens and shaped to engage a groove on the rim of an eyeglass frame to secure the lens in place. The lens incorporates a circumferential groove on its peripheral edge, which receives a tongue extending inwardly from the inner surface of the liner, for positioning the liner on the peripheral edge of the lens. Thus, the liner is engaged with the lens before the lens is positioned within the retention groove, which therefore still presents problems in use in terms of inserting the lens-liner assembly within the frame. Accordingly, this particular device is expressly designed to be used in frames that have rims configured for selectively opening and/or radially adjusting for accepting the lens therewithin before tightening the rim about the peripheral edge of the lens by means of the usual screw tensioning or the like. Thus, this particular device would very likely be substantially incapable of properly functioning in connection with molded eyewear having no means for selectively opening and/or radially adjusting the frame rim. In other contexts wherein complete and non-opening frame rims are to be employed along with such a liner or gasket, rather than pre-installing the liner on the lens, other prior art teaches only that the separately-formed liner may instead be somehow temporarily deformed and pushed into the lens retention grooves of the frame, which introduces additional complications in connection with positioning and retaining the liner in place and related concerns about its performance.
Therefore, there is still a need for an apparatus, as well as a method of manufacturing and using such an apparatus, that is configured for use in the molding industry and capable of both forming a groove-like undercut on an inner surface of a molded part while reducing the likelihood of damaging that molded part, as well as providing a relatively sufficient amount of cushion to accommodate the later insertion of a separately manufactured part within that undercut, without the apparatus moving out of position. Aspects of the present invention fulfill these needs and provide further related advantages as described in the following summary.